The present invention relates to a transmission for vehicles, and more particularly to a drum supporting structure in which a drum is rotatably supported on a sleeve a portion of which is loosely engaged with a shaft with clearance fit.
A conventional transmission includes a drum rotatably supported on a stationary shaft. A relatively large frictional stress is exerted on the shaft during rotation of the drum. In order to reduce the frictional stress on the shaft, there has been proposed a transmission in which the drum is supported on the shaft through a sleeve which is interposed therebetween.
Such a transmission is disclosed in a publication entitled "TOYOTA AUTOMATIC TRANSMISSION REPAIR INSTRUCTION A341E, November, 1989 (Vol. 63231)". The transmission includes a sleeve made of a wear resisting material and press-fitted onto a stationary shaft. A drum is rotatably supported on the shaft through the sleeve. Seal ring grooves are formed on a circumferential face of the sleeve in an axially spaced relation. The seal ring grooves receive seal rings therein.
However, upon press-fitting, the sleeve is radially expanded due to a tensile stress exerted thereon. Then, the seal ring grooves must be subject to a hoop tension which causes reduction in durability of the seal rings. If using the sleeve having an increased thickness or an increased length in order to enhance strength of the sleeve against the hoop tension, the transmission should be increased in weight or size. Alternatively, if the sleeve is subject to heat treatment for enhancement of the strength, a subsequent cutting for forming the seal ring grooves on the treated sleeve is not readily performed.